Radially firing pyrotechnic igniter



Sept. 15, 1964 S. S. LAIFMAN ETAL RADIALLY FIRING PYROTECHNIC IGNITER Filed Jan. 4, 1960 5 Sheets-Sheet 1 y ERNEST w. BRU

AARON HITCHENS may.

ATTORNEY p 1964 s. s. LAIFMAN ETAL 3,148,505

RADIALLY FIRING PYROTEICl-WIC! IGNITER Fild Jan. 4. 1960 s Sheets-Sheet 2 VIII/III STEVEN s.

BY AARON L.'H|TCHENS ATTORNEY p 1964* s. s. LAIFMAN ETAL RADIALLY FIRING PYROTECHNIC IGNITER 3 Sheets-Sheet 3 Filed Jan. 4, 1960 INVENTORS S LAIFMAN S. SACKS W. BRUMITT L.- HITCHENS FIG ATTORNEY United States Patent Ofi ice 3,148,505 Patented Sept. 15., 1964 RADIALLY FIRING PYRUTMIHNIC IGNTTER Steven S. Laifrnan, Los Angeies, Harvey S. Sacks and Aaron 1.. Hitchens, Northridge, (Iaiifl, and Ernest W.

llBrurnitt, London, England, assignors to North American Aviation, Inc.

Filed Jan. 4, 1960, Ser. No. 199 11 Claims. (Cl. 6il-39.82)

This invention relates to igniters for combustible materials and in particular to igniters having inherently desirable flame pattern characteristics for utilization in liquid propellant rocket engines.

Igniters heretofore known in the art of rocketry have experienced major difliculty in propagating a flame pattern capable of covering a significant area of the propellant injector face. The result has been a rough type of ignition wherein the propellants in only the immediate vicinity of the flame are initially ignited, with a subsequent spreading of the flame front over the balance of the area. Such rough rocket engine starts are many times sufficient to trigger combustion instability in the combustion chamber. This instability is many times eventually detrimental to thrust chamber construction, particularly throughout engine starting transients. This problem has become increasingly acute as the size of the rocket engine has increased, which likewise increases the injector face area over which propellants are injected into the combustion chamber.

The present injector includes structure inherently able to direct a flame radially outward in a 360 pattern. When the size and the combustion characteristics of the igniter pyrotechnic charge and the area of the injector face are properly proportioned, the igniter flame pattern covers essentially the entire face of the injector. When propellants are subsequently injected, ignition is prompt and simultaneous over the entire injector face, the result being a marked reduction in the tendency of the rocket engine toward combustion instability.

A second major igniter problem has been thrust chamber damage. This problem has been particularly apparent in regeneratively cooled thrust chambers constructed of thin walled, metallic tubes. The chamber damage has generally resulted from structural parts of the igniter being hurled against the thrust chamber tubes by high velocity gases existing in the chamber during or after the ignition stage. Such action has badly dented or actually perforated tube walls in many instances.

This difliculty has been materially overcome in the present igniter by providing a structure the bulk of which is consumed by the flames produced by the ignited propellants and by the igniter proper. After ignition is completed only a minimum of igniter structure remains to be ejected from the thrust chamber.

A third problem of prior art igniters has been their inability to function effectively after extended periods of storage, particularly under adverse conditions of humidity. The major problem in this respect has been in the difliculty experienced in obtaining an effective hermetic seal. The structural characteristics of the present igniter enable sealing with soldered joints. This has given the device the ability to function with a high degree of reliability after storage for over twelve months under highly adverse humidity conditions.

The new igniter is also constructed so as to initiate actuation of sequencing mechanisms in the rocket engine system at a predetermined instant, causing the introduction of propellants into the combustion chamber only after it has been assured that ignition conditions are proper to support combustion. This is accomplished by interrupting a normally complete electrical circuit, the interruption resulting from the action of flame issuing from the igniter and causing a break in a circuit segment disposed about the igniter body.

It is a major object of this invention to provide a rocket engine igniter eflicient of operation with minimal malfunction possibilities.

It is a further object to provide a rocket engine igniter with the capability of producing a radial flame pattern.

A further object is to provide an igniter having the ability to produce a flame front over a substantial area of the face of a rocket engine propellant injector.

Another object of the invention is to provide an igniter with a maximum of flame consumable and/or erodable structure.

Yet another object is to provide an hermetically sealed igniter capable of storage under adverse environmental conditions for extended time periods.

A still further object is to produce an igniter capable of providing a signal for the initiation of propellant iujection.

Other objects will become apparent from the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a partial cut-away of a regeneratively cooled rocket engine having a propellant igniter installed therein;

FIG. 2 is a sectional view of one embodiment of the igniter;

FIG. 3 is a sectional view of a second embodiment;

FIG. 4 is a partially cut-away perspective of the preferred embodiment of the invention;

FIG. 5 is a cut-away illustrating an alternate form of the ignition body of the FIG. 4 embodiment; and

FIG. 6 is a view taken along lines 6-6 of FIG. 5.

Referring to the drawings, FIG. 1 illustrates a regeneratively cooled rocket engine of a type to which the present igniter is particularly adaptable. The rocket engine, generally indicated as 1, has an igniter 2 screwed into the face of injector 3 internally of combustion chamber 4 upon the longitudinal axis of the rocket engine. Electrical leads are connected through the igniter from an electrical source (not shown) for ignition and component sequencing purposes.

A first embodiment of the pyrotechnic igniter 11 of this invention appears in FIG. 2. It includes a center post or support rod 12 having threads 13 on one of its ends for attachment to the rocket engine injector. A cap member or casing 14, preferably made from an erodable material, e.g. various plastics or Fiberglas, is supported upon rod 12 by a pair of snap washers 15 or other suitable holding means. A solid pyrotechnic mixture 16 is disposed within cap member 14 about rod 12 such that a single surface 17 of the pyrotechnic is exposed to the surrounding atmosphere and substantially radially disposed from rod 12. The pyrotechnic formulation forms no part of the present invention and a suitable composition will be readily apparent to the skilled pyrotechnist.

Adjacently exposed from the open end of cap member 14 is a deflector plate 18 supported upon rod 12 typically by snap washers 19. A plurality of pyrotechnic squibs 20 are retained within the annular space between surface 17 and plate 18. They are partially embedded in deflector plate 18 in this instance. Their position must be adjacent pyrotechnic surface 17 so as to initiate the combustion of that surface of pyrotechnic 16 when the squibs are ignited. Electrical leads 21 are connected to resistor wire 21a. Resistors Ztla are positioned to contact squibs 2t) and to cause squib ignition when electrically heated. The heating may be initiated by the closing of an electrical switch in the circuit at a remote location. A break link 22 is supported at a position intermediate pyrotechnic surface 17 and deflector plate 18 and is adapted to be burned through by the flame issuing from pyrotechnic 16 upon its ignition. This interrupts a normally complete circuit through electrical leads 23 and ground wire 21b connected between opposite ends of break link 22. The signal interruption is received by a conventional detector means in a position remote from the igniter and used to control rocket engine component sequencing as known in the art.

The overall operational sequence of the rocket engine to which the igniter is adapted is initiated by energizing the electrical circuit across squibs 20. This causes the squibs to ignite. Squibs are designed to generate sufii cient heat to ignite surface 17 of main igniter pyrotechnic charge 16. Combustion of charge 16 produces flame and extremely hot gases in great quantity, which issue forth from surface 17 with considerable force. The flame and gas impinge against deflector plate 18 and are deflected radially outward in a substantially flat sheet. Dependent upon the size of the components involved and the pyrotechnic used, they may cover the entire face of the injector to which the igniter is attached. Thus, the igniter produces a 360 flame pattern having inherently great capabilities of simultaneously igniting all portions of propellants subsequently issuing from the injector.

When the combustion of the pyrotechnic mixture has been fully established, break link 22 is burned through, interrupting the circuit of which it is a part. The resultant signal indicates that ignition conditions have been sufliciently established and the sequencing of the propellant injector valves is initiated for the introduction of propellant into the combustion chamber.

A cover or casing 24, supported upon rod 12 by washers 25, may be provided to protect the electrical circuitry connecting squibs 20 and break link 22 during initial combustion phases. Cover 24 may be separate from or integral with plate 18. It is preferable that deflector plate 18 and cover 24 also be made from an erodable material in order that they cannot be broken into pieces, or broken loose as a unit during engine firing and hurled against the thrust chamber walls. This eliminates chamber wall damage due to loose igniter structure.

An alternate igniter configuration appears in FIG. 3. Therein, an erodable or combustible head 31 includes a threaded stud 32 for attachment purposes. Electrical leads 33 are encased in a shielding 34 and are conducted into head 31 through a tube 35. They are connected to squibs 36 for the same purpose as described above with reference to FIG. 2. A cup member 37 is supported upon tube and pyrotechnic 38 is disposed about tube 35 within cup member 37.

A break link, as described with respect to FIG. 2, may also be used in the FIG. 3 modification.

One of the major problems in igniters for rocket engines is storability, the pyrotechnic being subject to deterioration when exposed to moisture. Hence, it is desirable that the pyrotechnic and the squibs be contained in an hermetically sealed compartment. This compartment is provided in the FIG. 3 igniter by a thin sealing member 39a circumferentially disposed about annular slot 39 defined between head 31 and cup member 37. Sealing member 39a is preferably a metal foil of extremely thin cross section. This foil is bonded or soldered in place and is readily burned away upon the initiation of pyrotechnic combustion, the flames then being allowed to issue from the igniter in a complete 360 radial pattern.

The preferred embodiment of this invention is illus trated in FIG. 4. This embodiment includes a minimum of structure which could be considered neither erodable nor combustible. Thus, an insignificant amount of material potentially detrimental to thrust chamber structure is present. This igniter, generally indicated as 40, is supported in the rocket engine injector by a heat resistant (may be metallic) attachment stud 41. It is held a desirable distance away from the injector face by erodable extension stud 42 and includes an internally threaded insert 43 adapted to accept a center post 44 upon which is supported the balance of the igniter structure. Disposed about center post 44 is central igniter body 45. This body is preferably made from an erodable material as specified with reference to FIG. 2. A pair of metal discs 46 and 47 are spaced from one another and molded or cast within igniter body 45 so as to extend radially outward therefrom. Disc 46 has an axially extending tubular member 48 attached about a perforation through its center. Similarly, a second tubular member 49 extends from disc 47 coaxially about tube 48. Discs 46 and 47 and tubular members 48 and 49 may be made from a material which is meltable under high temperature conditions, e.g. brass. Each tubular member may contain apertures 59 and 51 to facilitate molding or casting of the tubular members within body 45. Body 45 is disposed about and between the discs and tubular members, as illustrated. The material used is electrically insulating, and may be Diall No. 5201, which may be prepared in accordance with US. Government specification MILM- 18794, Type SDG. A series of cavities 52 are provided in the body material between the discs 46 and 47 Pyrotechnic squibs 53 are contained within cavities 52 and electrical resistance wires 54 (e.g. 80%-20% platinum iridium) are connected across the exposed face of the squibs from disc 46 to disc 47.

Glass seals 48a and 49a may be provided as hermetic seals at the ends of tubes 48 and 49.

Upper and lower cap members 55 and 56 extend radi ally outward from igniter body 45. Flanges 57 and 58 extend axially from caps 55 and 56 respectively and provide means to which a thin metal foil hermetic seal 59 may be soldered. Upper cap member 55 is centrally connected (soldered, screwed, etc.) to insert 43 through its central flange 60 which also serves to retain the unit in the igniter body. Similarly, lower cap member 56 has a central flange 61 connected to tubular member 48. For the purposes of this igniter configuration, it is preferable that cap members 55 and 56 and seal 59 each be made from an electrically conductive material in order that an electrical circuit may be completed through tubular member 48, cap member 56, seal 59, cap member 55, insert 43 and center post 44. This circuit serves the same function of the break link described in the FIG. 2 configuration, seal 59 serving as the destructable link for circuit interruption. A separate electrical circuit is completed through tubular member 49, disc 47, resistance wires 54, disc 46, and tubular member 48 to provide for the heating of resistance elements 54 and the ignition of squibs 53. Cap members 55 and 56 should also be relatively thin in cross section to minimize structure and readily meltable during engine firing to further reduce the hazard of flying debris. A .003 inch thickness of brass is acceptable for this purpose. Cap members 55 and 56 thus serve the dual function of providing portions of both an hermetic seal and an electric circuit. Seal 59 also serves these functions in addition to acting as the break link.

This embodiment of the invention utilizes a pair of spaced pyrotechnic charges 62 and 63, rather than the single pyrotechnic charge and deflector plate arrangement heretofore described. Each of the pyrotechnic charges 62 and 63 acts as the deflector for the combustion products from the opposite charge in achieving the radial flame pattern. The exposed surfaces of charges 62 and 63 are preferably serrated to provide a maximum of surface area for initial combustion.

A combustion-inhibiting material 64 covers all pyrotechnic surfaces except the exposed serrated surfaces where combustion is to be initiated. Material 64 serves the dual function of preventing pyrotechnic combustion in covered areas with the inhibitor and providing a humidity impervious layer about the pyrotechnic charge. A suitable material for this purpose is a heavy synthetic rubber compound such as PRC 1222, available from Products Research Corporation, which chemically cures to a tough, rubbery solid.

Electrical leads 65, 66, and 67 are soldered or otherwise electrically connected to tubular member 49, tubular member 48 and center post 44, respectively. They lead to remotely located switching and signalling means (not shown) for the purpose described above. These leads may be encased in a cable jacket 68 and a sheath 6? for protection during the initial phases of combustion. The volume 7 within sheath 69 may also be encapsulated with a commercially available potting compound.

A functional cycle of the preferred embodiment of the igniter is actuated through the closing of a switch (not shown) to energize the circuit described through resistance wires 54, causing squib 53 to be ignited. Squib 53 then ignited the serrated surfaces of pyrotechnic charges 62 and 63, the flames resulting therefrom being deflected against opposing surfaces and deflected radially outward. The flame burns through seal 59 causing an interruption of the electrical circuit therethrough and providing a signal to a detector means for the initiation of propellant injection. The propellants are effectively and efliciently ignited, providing a desirable environment for a rocket engine ignition phase which is smooth and stable.

An alternative configuration of central igniter body of the FIG. 4 igniter is illustrated in FIGS. and 6. This igniter body eliminates tubular members 48 and 49 of FIG. 4 by providing a pair of plated portions 71 and 72 for the inner electrical connections of plates 46 and 47. A pair of grooves 73 and 74 are provided longitudinally of the body, groove 73 extending through slot 47a in plate 47 to plate 46 and groove 74 extending to plate 47. The bottoms of the grooves are then plated with electrically conductive material 71 and 72, and a potting compound 76 applied over the plating except at exposed plated portions 77 and 78 at the lower body extremity. The newly applied potting material is then threaded to match the balance of the body. Portions 77 and 78 are electrically insulated from one another and from center post 44. An effective manner of applying this plating or printed circuit is to flush-coat electroless nickel within the grooves to a thickness of approximately .00005 inch as a base for a subsequent plating of electrolytic copper and a final coat of electroless gold applied directly to the copper. The copper serves as the main electricity-carrying element and the gold plating provides a corrosion resistant covering for the copper. The gold also facilitates soldering of electrical leads. A metal ring 79 may be sweat-soldered about the igniter body to assist in retaining the potting compound and to complete the electrical circuit.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by Way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. An igniter comprising a central body including means for attachment to supporting structure, a pyrotechnic charge disposed about said body, a squib for igniting said charge, and means adjacently spaced from said charge for directing combustion products from said charge into an essentially flat and continuous radial pattern, said directing means being constructed of a flame consumable material, said directing means and said charge cooperatively defining an annular slot therebetween for producing said continuous radial pattern.

2. The igniter as set forth in claim 1, wherein said central body includes electrical transmissive means for squib ignition and wherein a hermetic seal surounds said pyrotechnic charge, said seal including an electrically conductive flame consumable portion forming part of a complete electrical circuit, said portion being positioned to be consumed by said combustion products to provide an interruption of said electrical circuit.

3. The igniter as set forth in claim 1, wherein a major portion of the structure making up said igniter is constructed from flame consumable materials, a portion of said materials being erodable when exposed to high temperature and high gas velocity environment.

4. A radially firing pyrotechnic igniter comprising a pyrotechnic charge having a portion of its surface inhibited against combustion, means for igniting the portion of said charge not inhibited, and means for directing flames from said ignited pyrotechnic charge outward into a continuous radial flame pattern, said directing means being composed of flame consumable materials, said directing means and said charge cooperatively defining an annular slot therebetween for producing said continuous radial pattern, said igniter being constructed from materials substantially the total of which are combustion and erosion consumable upon exposure to flame and a high gas Velocity environment.

5. A radially firing pyrotechnic igniter comprising at least one pyrotechnic charge having a major portion of its surface inhibited against combustion and a portion not inhibited, ignition means for igniting said non-inhibited portion of said charge, means adjacent said non-inhibited portion for directing flames from said charge when ignited into an essentially flat and continuous radial flame pattern, said means being constructed of flame consumable materials, humidity insensitive means sealed about said charge to normally prevent communication between said charge and the surrounding atmosphere, and means upon said igniter for attachment to supporting structure.

6. The radially firing pyrotechnic igniter of claim 5, wherein two of said pyrotechnic charges are provided, each of said charges having said non-inhibited surface portion adjacently spaced from a similar non-inhibited surface portion on the other of said charges, said non-inhibited surface portions making up said means for directing said flames into a radial pattern.

7. The radially firing pyrotechnic igniter of claim 5, wherein said humidity insensitive means includes a metal foil peripherally sealed about said igniter.

8. A radially firing igniter for combustible fluids, said igniter comprising an elongated post containing means on one end thereof for attaching said post to a supporting structure; a pair of discs circumfenentially disposed about said post and fixed thereto, a surface of each of said discs being adjacently spaced from a surface upon the other of said discs, at least one of said discs being composed of solid propellant; combustion-inhibiting means covering the periphery of said solid propellant except for said adjacent surface thereof; the other of said discs being constructed of a flame consumable material an electrically actuatable combustion-initiating squib secured between said discs to ignite said solid propellant, and electrical means contacting said squib to ignite said squib, said igniter being substantially consumable by flame and high velocity gas erosion, whereby flame from said solid propellant impinges against said adjacent disc surface and is deflected outward in a substantially continuous radial flame pattern and said igniter and other disc is substantially consumed during operation of said igniter and a device to which it is applied.

9. A radially firing, pyrotechnic igniter comprising a heat resistant stud adapted for attachment to supporting structure; a flame-consumable extension attached to said stud and extending therefrom; an electrically conductive center post attached to and extending from said extension remote from said stud, the remote end of said post adapted to receive an electrical attachment; an elongated, flameconsumable igniter body radially disposed about said center post, a pair of adjacently spaced, electrically conductive discs embedded in said igniter body, said discs being electrically insulated from said center post and from one another, at least one combustion-initiating pyrotechnic squib mounted between said discs at the outer periphery thereof; an electrical heating element connecting said discs and in contact with said squib for igniting said squib; a pair of pyrotechnic charges circumferentially disposed about said igniter body and spaced by said discs, said pyrotechnic charges extending from said igniter body radially beyond said discs; a layer of combustion-inhibiting material intimately contacting all surfaces of said pyrotechnic charges other than adjacently opposed surfaces thereof; a pair of electrically conductive caps covering said combustion-inhibiting material about a portion of the circumferential peripheries and ends of said pyrotechnic charges remote from one another, one of said caps making electrical contact with said center post and the other of said caps electrically insulated from said center post; a sheet of electrically conductive metal foil sealably joined to said caps to cause their connection, said caps and said sheet forming an hermetic seal enclosing said pyrotechnic charges and cooperating to form a portion of an electrical circuit, one of said caps and a free end of said center post adapted to receive electrical connections adjacent their mutually insulated position; electrically conductive means connecting one of said discs and an electric terminal upon said igniter body adjacent said free end of said center post, electrically conductive References Cited in the file of this patent UNITED STATES PATENTS 2,419,866 Wilson Apr. 29, 1947 2,518,882 Goddard Aug. 15, 1950 2,667,740 Goddard Feb. 2, 1954 2,942,547 Rabern et al. June 28, 1960 FOREIGN PATENTS 876,965 Great Britain Sept. 6, 1961 

1. AN IGNITER COMPRISING A CENTRAL BODY INCLUDING MEANS FOR ATTACHMENT TO SUPPORTING STRUCTURE, A PYROTECHNIC CHARGE DISPOSED ABOUT SAID BODY, A SQUIB FOR IGNITING SAID CHARGE, AND MEANS ADJACENTLY SPACED FROM SAID CHARGE FOR DIRECTING COMBUSTION PRODUCTS FROM SAID CHARGE INTO AN ESSENTIALLY FLAT AND CONTINUOUS RADIAL PATTERN, SAID DIRECTING MEANS BEING CONSTRUCTED OF A FLAME CONSUMABLE MATERIAL, SAID DIRECTING MEANS AND SAID CHARGE COOPERATIVE- 